1. Field of the Invention
This invention relates to an electrical socket for interfacing an integrated circuit to a printed circuit board, and more particularly to a surface mounted pad array socket for receiving an integrated circuit housed within a pad array integrated circuit chip carrier.
2. Description of Related Art
The prior art includes a number of sockets for electrically interconnecting integrated circuits (or "IC") to printed circuit (or "PC") boards. The principle objectives of such sockets are to electrically interconnect the electrical contacts of an IC to corresponding electrical contacts on the PC board and to mechanically fix the IC to the PC board.
In the past, integrated circuits had relatively few contact points. (A contact point is any point through which electrical current flows between an IC and a PC board.) However, as ICs have grown in sophistication and complexity, the number of contact points has increased. Consequently, the requirements of the sockets used to interconnect an IC to a PC board have changed.
A common means for interconnecting integrated circuits to PC boards is to install an IC in an integrated circuit carrier. An IC is electrically connected to the carriers conductive leads, which have relatively large dimensions, by fine wires. Typically, these wires are gold bonded to the IC. The leads provide electrical contact points external to the IC carrier. The relatively large dimensions of the leads make them relatively easy to solder to a PC board. Soldering the leads to a PC board serves the dual function of mechanically securing the IC carrier to the PC board and forming electrically conductive pathways between the PC board and the IC.
Manufacturers have developed a number of standard packages for ICs. One such package is known as a pad array IC carrier (carrier). The carrier has a large array of contact points on its bottom surface. The carrier may be placed over and soldered to an array of corresponding contact pads on a PC board that mirror the array of contact points on the carrier.
However, the greater the number of contact points on an IC carrier, the more difficult it is to solder the IC carrier to a PC board. Additionally, it is frequently desirable to be able to remove an IC from a PC board without having to unsolder the IC carrier. Since it is desirable to be able to remove and replace ICs previously installed, a variety of apparatus have been invented to interconnect an IC carrier to a PC board without directly soldering the carrier to the PC board. One such apparatus is described in U.S. Pat. No. 4,658,331 issued to Berg.
The Berg apparatus uses a flexible circuit upon which an IC is mounted. The IC is soldered to the flexible circuit. The flexible circuit and IC are fitted with a strain relief member to give form to the flexible circuit and to protect the solder joints between the flexible circuit and the chip from excessive stresses. The flexible circuit, IC, and strain relief member are then placed upon a PC board. Electrical contact pads of the flexible circuit make contact with corresponding electrical contact pads on the PC board. A backing frame is positioned on the opposite side of the PC board. The flexible circuit, strain relief member, and backing frame are secured to the PC board by screws. Compressive forces established by the screws cause the flexible circuit contact pads to maintain an electrical connection with the PC board contact pads without the use of solder.
In another apparatus, described in U.S. Pat. No. 5,018,005 issued to Lin et al., electrical connections are made between an IC and a flexible circuit element. The IC, along with the flexible circuit, are packaged to protect the IC. The flexible circuit element extends from the central region of the package and is soldered to a PC board for the purpose of transmitting electrical signals between the IC and the PC board.
A continuing goal of practitioners in the art of IC packaging and design is to create a means to easily mount an IC onto, and dismount the IC from, a PC board. Additionally, in many cases it is desirable for an IC package or socket to be mounted entirely on the surface of a single side of a PC board. Packages such as that described in the Lin patent are mounted entirely on one side of a PC board. However, the IC is difficult to replace in the field once mounted to a PC board. The IC cannot be removed from the package, and the package is soldered to the PC board. Therefore the package must be unsoldered to remove and replace the IC. The process of unsoldering a package from a PC board requires a certain degree of skill. Even when a person of relative skill performs the unsoldering, the PC board and/or IC package are at risk of being damaged. Furthermore, the process of unsoldering takes a relatively long time. Although sockets such as that described in the Berg patent do not require unsoldering to replace an IC, hardware must be mounted on both sides of a PC board.
Therefore, there is a need for an IC socket for use with an IC mounted in a pad array carrier from which the IC carrier can easily be removed without the need to unsolder the IC carrier or the integrated circuit socket from a PC board. The present invention provides such an IC socket.